New signing Demba Ba marked his Chelsea debut with a brace as Rafael Benitez’s side beat Southampton 5-1 in their FA Cup third-round tie at St Mary’s.

The Senegalese striker's instantaneous impact was in sharp contrast to Fernando Torres' slow start at the club with the Spaniard taking 25 games to reach two goals after his move from Liverpool.

Chelsea, who have won the FA Cup in four of the last six years, slipped behind in the 22nd minute as Jay Rodriguez produced a composed finish to put the hosts in front, but Nigel Adkins's side's advantage did not last for long.

Southampton came into the match having won their four previous FA Cup meetings with Chelsea, but their lead was cut short in the 36th minute as Ba levelled the scores from a yard out to make an early impact following his move from Newcastle, before Victor Moses lashed home a volley and Branislav Ivanovic netted a third.

Ba netted a second just after the hour mark with a tidy finish at the near post to double his tally, and Benitez’s side were able to cruise through the second half with substitute Frank Lampard making it five from the penalty spot late on to round off the victory.

Lampard's goal saw him became Chelsea's joint second highest goal-scorer ever alongside Kerry Dixon on 193 career goals for the London club. Bobby Tambling leads the way with 202 goals.

New signing Ba was handed a start as the 27-year-old striker replaced Torres in one of five changes made by Benitez from the 1-0 derby defeat to QPR; Adkins, meanwhile, made two changes with James Ward-Prowse and Rodriguez replacing Gaston Ramirez and Rickie Lambert, respectively.

Ba threatened for the first time in the match as he ghosted past his marker Maya Yoshida before cutting the ball back from the by-line, but his delivery ran straight to Jose Fonte, who was able to coolly clear upfield.

The hosts made a bright start to the match, and their inventive forward play was rewarded in the 22nd minute as Jason Puncheon slipped a sublime through ball beyond Gary Cahill and into the path of Rodriguez, who netted his fifth goal of the season with a precise toe poke beyond Ross Turnbull.

Chelsea immediately pushed forward with real urgency, and Eden Hazard was inches away with a precise curled shot towards the far corner of Artur Boruc's goal four minutes after the opening goal as he and Juan Mata caused havoc in the final third.

The visitors proceeded to bombard the Southampton box with crosses from both flanks, but it was a run from Mata - who scored four and assisted four goals for Chelsea in the FA Cup last year - that led to the equaliser for the visitors. The Spaniard scooped the ball over the onrushing Boruc with a deft touch, and the opportunistic Ba was on hand to tap the ball in from on the goalline to mark his Blues debut with a goal – his 14th goal of the campaign.

After just seven minutes of the second half, Chelsea had secured a two-goal cushion as Mata clipped another pinpoint delivery into the box from the left, and Ivanovic was perfectly placed to head powerfully beyond Boruc for his sixth goal of the season.

Steve De Ridder came on to provide a more attacking option for the hosts with Morgan Schneiderlin making way just before the hour mark, but Chelsea continued to overrun their opponents in the midfield with Mata imperious in the final third.

Three of the four previous FA Cup clashes between the two sides have gone to a replay, but the tie was effectively ended as a contest in the 61st minute as Ba bagged a second to double his tally on debut with a neat finish at the near post as he met a pinpoint cross from Hazard out on the right.

Southampton's misery was compounded as central defender Fonte had to be stretchered off, with Jos Hooiveld coming on in his place, while Chelsea were afforded the luxury of making changes with Lampard among those introduced in the second half.

Ba was brilliantly denied a hat-trick late on as Boruc produced a very fine reflex stop with his legs to save a powerful downward header, but Lampard made it five from the penalty spot after having come on for the last half hour with Yoshida harshly adjudged to have handled the ball in the box.

Southampton have now lost 15 of their last 19 FA Cup matches against sides in the top flight and must now switch their attention to their fight for Premier League survival, while Chelsea secured an important win as Benitez chases silverware for the European champions.

MAN OF THE MATCH

Juan Mata – Chelsea: While Demba Ba scored twice on his debut, it was the imperious Mata who made everything tick for his side, and the Spaniard was at the forefront of everything in the final third for the visitors.